1. Field of the Invention
This invention generally relates to wireless communication and, more particularly, to wireless communication antennas.
2. Description of the Related Art
The size of portable wireless communications devices, such as telephones, continues to shrink, even as more functionality is added. As a result, the designers must increase the performance of components or device subsystems and reduce their size, while packaging these components in inconvenient locations. One such critical component is the wireless communications antenna. This antenna may be connected to a telephone transceiver, for example, or a global positioning system (GPS) receiver.
Wireless communications devices are known to use simple cylindrical coil or whip antennas as either the primary or secondary communication antennas. Inverted-F antennas are also popular. Many conventional wireless telephones use a monopole or single-radiator design with an unbalanced signal feed. This type of design is dependent upon the wireless telephone printed circuit boards groundplane and chassis to act as the counterpoise. A single-radiator design acts to reduce the overall form factor of the antenna. However, the counterpoise is susceptible to changes in the design and location of proximate circuitry, and interaction with proximate objects when in use, i.e., a nearby wall or the manner in which the telephone is held. As a result of the susceptibility of the counterpoise, the radiation patterns and communications efficiency can be detrimentally impacted. Even if a balanced antenna is used, so that the groundplanes of proximate circuitry are not required as an antenna counterpoise, radiation pattern and radiation-susceptible circuitry issues remain.
This problem is compounded when an antenna, or a group of antennas operate in a plurality of frequency bands. State-of-the-art wireless telephones are expected to operate in a number of different communication bands. In the US, the cellular band (AMPS), at around 850 megahertz (MHz), and the PCS (Personal Communication System) band, at around 1900 MHz, are used. Other communication bands include the PCN (Personal Communication Network) and DCS at approximately 1800 MHz, the GSM system (Groupe Speciale Mobile) at approximately 900 MHz, and the JDC (Japanese Digital Cellular) at approximately 800 and 1500 MHz. Other bands of interest are GPS signals at approximately 1575 MHz, Bluetooth at approximately 2400 MHz, and wideband code division multiple access (WCDMA) at 1850 to 2200 MHz.
To dampen the effects of radiation upon proximate circuitry it is known to attach so-called bracket, or radiation-parasitic, elements to a groundplane. Typically, these “brackets” are used to evenly distribute current through the groundplane associated with a radiated wave. Alternately stated, the brackets are used to prevent any particular spot on a circuit board, chassis, or keyboard from becoming too sensitive to radiation-induced current. It is difficult, if not impossible, to design a wireless device to minimize the interaction between antenna radiation and susceptible circuitry in every one of its communication bands. As a result, a conventional design must be optimized for one particular communication band, or the design must be compromised to have for some (minimal) effect in every communication band of interest.
It would be advantageous if groundplane sensitivity to radiation-induced current could be minimized for every frequency of operation.
It would be advantageous if groundplane sensitivity to radiation-induced current could be tuned in response to changes in frequency, or in response to one particular area becoming too sensitive.
It would be advantageous if radiation desensitivity brackets could be made reconfigurable, to minimize the sensitivity of proximate circuitry at every frequency of radiation.